This proposal is designed to elucidate the primary structure of a large (Mol Wt. approximately 88,000) nonsuppressible insulin-like protein (NSILP) which is found in human serum in trace quantities. In order to achieve this objective large-scale purification strategies have been developed in collaboration with the American Red Cross Blood Fractionation Center. The purpose of this research objective is to obtain a clear undrstanding of the structural relationship between NSILP and insulin, and other smaller sized insulin-like proteins in serum. A second objective is to understand the physiological role of NSILP. In order to accomplish this in part a specific immunoassay for NSILP quantitation in biological fluids has been developed and is utilized in conjuction with a bioassay to study alterations in serum levels in human volunteers undergoing oral glucose tolerance testing, and in humans with various disorders of growth and/or metabolic fuel homeostasis. In particular, elevated levels of serum NSILP appear to be associated with some tumor hypoglycemic syndromes. Finally, a third objective is to determine the hepatic production of NSILP and its regulation by employing isolated rat liver perfusion techniques. If hormonal regulation by employing isolated rat liver perfusion techniques. If hormonal regulation of hepatic production of NSILP can be defined, then perhaps pharmacological strategies for modulating the serum level of NSILP can be developed, if such modulation is envisioned to be beneficial.